This invention relates generally to a socket for removably mounting an electronic part that has a large number of terminals on its lower surface in order to electrically connect each terminal to a circuit path which in turn is connected to test equipment for testing such electronic parts and more particularly to sockets of the type which employ a flexible contact sheet or film as a contact interface member.
It is conventional to subject semiconductor (IC) packages having resin sealed IC chips to various tests including a reliability test, called a burn-in test, to identify packages which do not meet required specifications. One such socket for use with semiconductor packages having terminals arranged in a Ball Grid Array (BGA) is shown in FIG. 8. As shown in the figure, socket 101 has a rectangular base 102 and a cover 103 pivotably mounted on the base and being movable between an opened position away from the base and a closed position engaged with the base. A contact film support 105, capable of supporting a contact film 104, to be described later, is provided at the central part of base 102. A thin flat rubber sheet 106 is disposed in a recessed portion formed on the upper surface of support 105. Compression coil springs 107 disposed between support 105 and base 102 provide an upwardly directed bias to support 105.
With reference to FIG. 9, a generally square shaped contact film 104 has a plurality of inner conductive pads 104b arranged at the center of the film in conformity with the pattern of solder balls 108a of BGA package 108. Inner pads 104b are respectively connected to outer conductive pads 104d arranged along the outer peripheral part of film 104a through a selected wiring pattern 104c. 
Again, with reference to FIG. 8, an adapter 109, capable of seating BGA package 108 with solder balls 108a exposed in an opening in the adapter, is removably provided on support 105 of base 102. Adapter 109 is placed over contact film 104 with the inner pads 104b of contact film 104 disposed at the opening of the adapter and with the outer peripheral part of the contact film bent by rib 109a of the adapter into a recess 102a formed in the base. The outer peripheral part of the contact film is received between rib 109a and contacts 111 mounted in the recess with the outer pads 104d electrically connected to respective contacts 111. Thus, an electrical connection is made from solder balls 108a to inner pads 104b which are connected by wiring pattern 104c to outer pads 104d and then to contacts 111 which in turn are connected to external substrate 110.
Cover member 103 has a compression member 112 for engaging adapter 109 as well as a BGA package 108 received in adapter 109. Compression member 112 is biased in a direction away from cover member 103 by means of a compression coil spring 113.
A BGA package 108 is arranged on contact film 104 through the opening in adapter 109 and cover member 103 is then closed, thereby causing the solder balls 108a of the BGA package and respective inner pads 104b of the contact film 104 to be connected with a compressive force applied from both base 102 through support 105 and cover member 103 through engagement portion 112. In the prior art socket described above, rubber sheet 106 which is interposed between support 105 and contact film 104 is plastically deformed when it is heated in a compressed state in connection with burn-in tests, thereby adversely affecting the effectiveness of the desired function of elastically receiving BGA package 108 and contact film 104 between support 105 and engagement member 112. As a result, it has been difficult to produce a suitable pressure between solder balls 108a of BGA package 108 and respective inner pads 104b of contact film 104 by merely employing the compression coil springs 107 and 113 through support 105 and engagement member 112. Further, with respect to contact film 104 used in the prior art socket, it has been necessary to arrange the same number of inner pads 104b and outer pads 104d as the solder balls 108a of the BGA package as well as the number of interconnecting paths between respective inner and outer pads. As the number of the solder balls of BGA package 108 increase, the inner pads 104b of the contact film are made smaller, thereby making it more difficult to form a wiring pattern 104c on contact film 104. Although it may be possible to form the contact film as a multi-layer substrate in order to facilitate forming the interconnections, such a substrate reduces flexibility, thereby making it unsuitable for use in this kind of socket.
It is an object of the present invention to provide a socket free of the above described prior art limitations. Another object of the invention is the provision of a socket in which the electrical connection between the terminals of an electronic package and the contacts of an interface contact film are optimized. Yet another object is the provision of a socket having an interface contact film particularly adapted for electronic packages having a large number of terminals.
A socket made in accordance with a preferred embodiment of the invention comprises a base wherein electrically conductive contact members capable of contacting each terminal of an electronic package having terminals arranged according to a selected pattern and a plurality of electrically conductive spring contact elements capable of applying force to the contact members from below are mounted and aligned respectively with each terminal of the electronic package. A compression member capable of moving in a direction either toward or away from the base is provided for applying a force from above tending to compress the spring contact elements.
According to a feature of the invention, the contact members are mounted on an interface contact film which is received on a surface of a support member which is also formed with a plurality of bores therethrough in alignment with the contact members of the contact film. The electrically conductive spring contact elements are in the form of a coil spring received in each bore and adapted to apply a force to each contact member of the contact film from below.
According to another feature of the invention, an adapter is provided capable of accommodating an electronic package and exposing the package terminals and each of the contact members. The terminals of the electronic package are connectable with the contact members of the interface contact film which is arranged between the adapter and the base, and a cover is provided that has a compression member capable of applying a force to the electronic package against the spring contact elements. The cover is mounted on the base and is pivotable between opened and closed positions in linkage with the compression member.
According to another feature of the invention, an inter-terminal pitch expansion substrate can be installed in the socket. The substrate has a plurality of terminals spaced apart a distance greater than the distance between the terminals of the electronic package inter-connected to the spring contact elements through a selected wiring pattern on the substrate.
According to yet another feature of the invention, the spring contact elements comprise a first axial length coil portion having a selected outer diameter and a second axial length coil portion having an outer diameter which is greater than the outer diameter of the first coil portion. The plurality of bores formed through the support member for receiving the spring contact elements have a first bore portion formed larger than the outer diameter of the first axial length portion and a second bore portion having a diameter formed somewhat smaller than the outer diameter of the second coil portion allowing fixation of the second coil portion in a respective bore of the support member while allowing free movement of the first coil portion and making it easier to install the spring contact elements.
According to a feature of the invention, the contact members of the interface contact film have a terminal engagement part formed in such a manner as to be engaged with a package terminal in conformity with the configuration of the terminals of the electronic package and, at the same time, have a contact engagement part for contacting a flattened end of a respective spring contact element.